Hitherto, a liquid crystal display element has been widely utilized as a color display element. Furthermore, because a liquid crystal display element can be driven by a low consumed electric power, recently, the application thereof to a display portion such as portable instruments, etc., has been positively investigated. Now, a color liquid crystal display element is largely classified into two kinds of a transmission-type liquid crystal display element and a reflection-type liquid crystal display element.
The transmission-type liquid crystal element is generally constituted of a dimming layer formed by enclosing a TN (Twisted Nematic) liquid crystal, an STN (Super Twisted Nematic) liquid crystal, or a ferroelectricity liquid crystal, etc., between a pair of polarizers, and a color filter layer.
However, a general color filter has a low light transmittance (from about 20 to 30%) and as the result thereof, the light utilization efficiency of the liquid crystal display element becomes 10% or lower. Thus, to display images having a sufficient luminance, a back light of a high luminance, such as a cold cathode ray tube, EL, LED, etc., is usually disposed at the back side of the transmission-type liquid crystal display element. However, because a back light has a high consume electric power, when a back light is applied to a portable instrument such as a transmission-type liquid crystal display element, etc., there is a problem that the driving time by a battery becomes short. Also, when an environment is bright, such as out-of-door, the visibility thereof is lowered and further, because a polarizing plate is used, there is a problem that the angle of vision is narrow.
A reflection-type liquid crystal display element is a liquid crystal display element aiming at saving an electric power used, utilizing in out-of-door, and increasing a visibility as a hard copy, without using the above-described back light. As the reflection-type liquid crystal display element, according to the kind of a liquid crystal used, there are known an ECB (Electrically Control Birefringence) mode, GH (Guest Host) mode, a TN mole, an STN mode, etc. The reflection-type liquid crystal display elements of the TN mode and the STN mode have almost a similar construction to the above-described transmission-type liquid crystal element but are equipped with a light reflection electrode in place of a back light. However, because a color filter and a polarized plate are used as in the transmission-type liquid crystal display element, the reflectance is generally low as about 10% and the display becomes dark. Thus, by the improvement of the light-reflection electrode or the utilization of a microlens, the brightness of about 30% as reflectance is obtained at a specific narrow visual angle. However, there are problems that the brightness is yet insufficient, the angle of vision is extremely narrow, and the visibility is inferior.
The reflection-type liquid crystal display element of the ECB mode is a liquid crystal display element of carrying out a color display by an interference color using a polarizer, and in the reflection-type liquid crystal display element, a color filter is not required and the brightness of the displayed images can be improved to some extent as compared with the reflection-type liquid crystal display elements of the TN mode and the STN mode but the problem that the visibility is bad has not yet been solved.
In the reflection-type liquid crystal display element of the GH mode, because a liquid crystal having a mixture of dichromatic dyes (GH liquid crystal) is used, a polarizer and a color filter are unnecessary and a bright display having a broad angle of vision becomes possible. However, there are problems that the design of the liquid crystal materials for obtaining a necessary contrast is difficult, the durability of dyes is bad, and also a construction of three liquid crystal layers corresponding to the colors of C (cyan), M (magenta), and Y (yellow) becomes necessary for a full-color display, which results in greatly increasing the cost of the element.
For the purpose of improving the light utilization efficiency, which is considered to be a theme in the display technique of using a color filter, a technique of making changeable the amount of the transmitting light of color filter is proposed. For example, Japanese Patent Laid-Open No. 48675/1998 proposes a technique of laminating plural piezoelectric thin layers and changing the thickness of each layer by an external electric field, whereby the wavelengths of the reflected light and the transmitted light are changed by an interference action. However, in the technique, because an interference action is used, there are problems that a visual angle reliance occurs, the width of wavelengths is narrow, the quantity of light is small, etc.